Method for continuously controlling the texture and crystallization of fluid food materials

ABSTRACT

A process and apparatus for continuously controlling the crystallization of material systems in particular fat containing substances, such as chocolate masses by a thermal treatment which entails cooling and heating. The cooling process is far stronger than under the traditional procedural method, is in fact so strong that under static conditions it would cause the material system that is to be processed to solidify and harden spontaneously. This solidification is prevented by a heating process which uses mechanical energy resulting from shear stress, in a shear flow, where the introduction of mechanical energy and hence the local temperature are spontaneously and sensitively adjustable. This permits the achievement of particular pre-determinable crystal modifications, and hence of specific desired properties in the final product. The treatment states place within a mechanism consisting of a cylindrical container and a rotor, driven rotationally, whose rotational speed is adjustable. Between a cooling jacket and the rotor is a shear gap, in which the mechanical energy for the production of heat is transferred to the material system that is to be processed. The energy transfer is for practical purposes adjustable without any time delay. Crystallization times are sharply reduced, rendering the entire mechanism smaller and more economical to operate. Only one tempering (or temperature) zone is necessary. The product leaves the apparatus at processing temperatures with a defined viscosity.

BACKGROUND OF THE INVENTION

The invention pertains to process and an apparatus for continuouslycontrolling the texture, in particular the crystallization, of materialsystems in the fluid state, in particular fat containing substances,such as chocolate masses. This is accomplished through a thermaltreatment by cooling and counteractive heating wherein the cooling isdone to such an extent that when the material system is in a state ofrest it spontaneously solidifies, and that heating is done by means ofenergy dissipation through a mechanically adjustable energy supplyresulting from shearing stress.

The contents of many food products include, among other raw materials,varying percentages of animal and/or vegetable oils and/or fats, orcombinations of these (for example chocolate, butter and margarine), incrystallized form.

The final products owe their essential and characteristic properties tothese crystallizable material systems.

Until now, crystallizable material systems have been frequently cooledin thermally controlled scraper heat exchangers or in double-walledcontainers (with jacket cooling, and an agitator equipped withscrapers), undergoing mechanical blending at temperatures below theirfreezing point, with variable efficiency in terms of speed. Most fatsand fatty mixtures have the property of forming various polymorphicstructures of their fatty crystals with different configurations oftheir fatty molecules (for example in the case of cocoa butter, α, γ,β', and β-crystal modifications). The stability of these crystalmodifications differs widely, and is responsible for the consistency,texture, surface luster (for example in chocolate) and mechanicalproperties of the final product (hard-soft, short-long structure,plastic/elastic-brittle, sticky-dry, gritty-smooth).

With the machines and types of apparatus that have been known up untilnow, temperature and duration control, as well as temperature gradientsduring cooling and reheating are only regulated on an empirical basisfor different kinds of matter systems. Hence the particular fixedcrystal modifications for the achievement of specific properties canonly be obtained fortuitously.

One such apparatus is known, for example from DE-PS 39 13 941 and EP-OS289 849.

As a measure of the blending intensity involved, shear gradients of from500 to 4000 s⁻¹ are produced. With regard to the square of the number ofrotations and hence the shear gradient dependent dissipated mechanicalenergy, this means a maximum difference in conditions of up to a factorof 64. Deliberately introducing mechanical energy while the highlysensitive crystallization processes are reaching fruition is out of thequestion here.

In addition, the significance of the size of "shear gradients" islimited to laminar layer flows, which means that the quantification usedhere of a "blending vortex" cannot properly be described by means ofdata about the shear gradient.

In this context it has not previously been thought to use a targetedsupply of dissipated mechanical energy as a "heat source" as well as astructure-inducing means of non-vorticized, genuine shear flow.

From the earlier, non-published DE-P-41 03 575.5 a procedure is knownfor cream or butter crystallization which produces a more easilyspreadable final product. This procedure works by introducing mechanicalenergy into a so-called "shear gap crystallizer", consisting of anexternal cylinder and a concentric internal cylinder which isrotationally driven.

What this model presents is the introduction of a constant supply ofmechanical energy, for uniform and homogeneous blending purposes. Thereis no notion of an energy-dissipation-controlled operating method usingcontrol of number of revolutions. As in other crystallization proceduresof the traditional kind, the thermal regulation of the operation takesplace solely through appropriate temperature adjustment by means of aheating or cooling agent.

The invention's central task is to produce a process and apparatus asdesignated at the outset, which make possible the achievement of crystalmodifications according to desired specifications, and hence ofparticular desired properties in the final product, in such a way as tobe reproducible.

This task is essentially performed by means of process and an apparatusdesigned to carry out this process which are hereinafter described.

In practical terms, the present invention calls for a shearcrystallization, conducted at a low temperature; in other wordscrystallizable material systems are subjected to a mechanically inducedlow-temperature crystallization. Cooling takes place, as directed by theinvention, at crystallization temperatures that are extremely lowrelative to the state of existing technology. Using "counter-control",by the application of heat with the help of the uniform and homogeneousintroduction of mechanical energy, an astonishingly flawless product isachieved with predominantly stable crystalline forms and within asharply reduced time-frame. Heating by means of the introduction ofmechanical energy takes place immediately and without any mentionabledelay for all practical purposes. This makes possible an appropriatelysensitive control mechanism, measuring for instance the viscosity of thematerial system that is being processed.

In other words, the cooling of the material system that is to becrystallized takes place to such a massive extent, according to theinvention, that the system would spontaneously solidify and harden understatic conditions as a material system. Through the introduction ofmechanical energy, which proceeds with uniform homogeneity because ofthe gap geometry that has been effected, energy is dissipated withregular uniformity in the material system. This leads to the heating ofthe material system, which counteracts the spontaneous crystallizationwhich would otherwise result from the low cooling temperature.Simultaneously the shear flow, at the low temperature levelsdeliberately selected for this reason, has the particular effect ofcausing distinct orientation conditions to be initiated formacromolecular components, which thereafter adopt what are apparentlypreferred "positions" for the formation of crystalline structures. Theshear induced alignment of molecular units, and likewise thesimultaneous extreme supercooling that takes place on the contact wallof the container, bring about an extremely sharp acceleration ofseed-crystal formation and crystal growth.

In contrast to the state of the art, the present invention achieves ahomogeneous introduction of mechanical energy as a result of thecharacteristic feature of its construction, namely a constant shear gapdistance over the entire stressed cross section. The effect of this isthat at any point on the shear gap in which the substance that is to becrystallized is subjected to stress, the introduction of mechanicalenergy is in an exceptionally strict sense constant; in other wordsenergy is dissipated regularly and simultaneously in the materialsystem.

The rapid seed-crystal formation leads to a large number of seeds, henceprevents the formation of a small number of large-size crystals (thislarge-growth pattern means a gritty final product). Besides, thepredominance of the formation of the desired stable or unstable crystalmodifications while the material system is undergoing polymorphiccrystallization can be regulated to fixed specifications, using theintroduced shear-energy. The sharply accelerated crystallizationkinetics generated by the invention's prescribed mechanism means thatsmall "reaction volumes" (free crystallizer volume-capacity) can beproduced, through which flow can continuously pass. Shortercrystallization times are required for specific, fixed material systems,also smaller heat-exchange surfaces and reaction containers, and lesscooling energy and less electrical energy, because smaller vessels arebeing used. Material systems investigated by way of examples from thearea of fats (namely cocoa butter) exhibit crystallization times which,relative to crystallization treatment of the traditional kind, areshorter by a factor of more than 100.

The regulating process is by no means a slow-moving operation, but withno difficulty it can occur with the requisite speed and sensitivity toensure a regular and uniform product. According to the invention'sprescribed mechanism, this is done by adjusting the setting of therotor's revolutions. This adjustment, short-term and massive, can be setto any degree desired, making for an extremely brief manipulation of theenergy conditions in the shear gap. Determining a specific introductionof mechanical energy depends on the product's retention-time in the gap,i.e. its gap geometry, as well as the product-volume flow and the numberof revolutions of the shaft.

The term "shear flow" as used in this description, means a smooth flowin which the molecular components of the material system are moved andaligned in parallel "layers" relative to one another. This alignmentproduces projected positions for the system's material components (suchas fatty molecules) in relation to each other, making it easier to"latch" into a crystal lattice. This substantially speeds up thecrystallization kinetics.

Provided the apparatus is developed according to the invention'sspecifications, as stated herein, fullest benefit can be drawn from theintroduction of mechanical energy as a standard regulating parameter forcrystallization conditions. Depending on a specifically fixed startinglevel for viscosity, the apparatus is so to speak"viscosity-controlled", namely by means of modifications made to theintroduction of mechanical energy, in other words the setting of therotor's revolutions.

The container's wall is "strongly cooled", as per the invention'sprescription. During this process the danger of "freezing up" isavoided, since the substance that is to be crystallized is only allowedto experience "low-temperature shock" on the contact surface. Hence itforms seed-crystals at a rapid rate; but these seed-crystals thengenerate a blend temperature in combination with the substance that hasnot come into contact with the wall, and this prevents a rapidre-solidification and re-hardening. The introduction of mechanicalenergy needs to be apportioned so as to ensure that an over-stronglocalized heat-up is avoided, in order to inhibit the desired stablecrystals that have already formed from re-melting.

Compared to the well-known procedural method for obtaining thecrystallization of a multiplicity of macromolecular material systems,the mechanism specified by this invention yields substantial timeadvantages (by up to a factor of 100), as well as considerable economicadvantages, due to the reduction in capital investments which is broughtabout by the markedly reduced crystallizer volume-capacity.

In principle only one temperature adjustment zone (or temperature zone)is really necessary, namely cooling alone, as against the 2-3 zones(cooling and heating) required by the familiar mechanisms that have beenin use to date. The pre-crystallized substance leaves the mechanism witha specifically fixed viscosity, and in a state directly susceptible toprocessing and finishing (no subsequent reheating is needed).

Hereinafter the invention is explained and elucidated in greater detail,with reference to the design, with the aid of a basic main sketch andaccompanying examples by way of illustration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the operating cycle.

FIG. 2 shows the crystallizer schematically represented in FIG. 1, inlongitudinal section.

FIG. 3 shows melt enthalpy graphs for cocoa butter as a sample product.

FIG. 4 is a chart for "cocoa butter" as an example, plottingretention-time in the crystallizer as a function of the coolingtemperature, for given viscosity settings.

SUMMARY OF THE INVENTION

The invention provides a process for continuously controlling thetexture and crystallization of food material systems in the fluid state,which comprises thermal treatment by cooling and counteractive heating,wherein the cooling is effected to such an extent that when the materialsystem is in a state of rest it spontaneously solidifies and thatheating is effected by means of energy dissipation through amechanically adjustable energy supply resulting from shearing stress.

The invention also provides an apparatus for continuously controllingthe texture and crystallization of food material systems in the fluidstate, by thermal treatment which comprises means for effecting thermaltreatment in a continuous flow container, including cooling which iseffected by means of the container wall and heating by means of a supplyof mechanical energy provided by a revolving rotor which, with thecontainer wall forms a gap for the transfer of shearing stress to thematerial system, and means for adjusting the rotational speed of therotor for the direct control of mechanical energy supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus schematically represented in FIG. 1 consists of atemperature-adjusted container with a stirring device as a priorholding-site for the material system, in this instance cocoa butter. Bymeans of a pump 2, the substance that is to be processed reaches thecontainer or crystallizer 4, which can also be designated as a"low-temperature shear crystallizer". In the crystallizer 4 there is arotor 21 set up (see FIG. 2), which is driven rotationally by a motor 3.The crystallizer 4 displays a cooling jacket with a cooling cycle 5.

The substance that is being processed passes via a main line 6 to athree-way valve 7 and from there either to the product flow 8 or to thereturn-outlet 9, in which a heat exchanger 10 is in place.

A bypass line runs in parallel to the main stream 6, with an intake at11 and a return-outlet at 12. This duct leads to a viscosity gauge 13with an on-line viscosity meter 14. Control and regulation are conductedby means of an appropriate unit at 15. Cooling is controlled at 16,number of revolutions at 17, and the substance flow at 18. The pump forthe viscosity gauge 13 is marked as 19.

The diagram in FIG. 2 shows a cross-sectional drawing of the containeror crystallizer 4. This consists of the rotor 21 with an accompanyingflat spiral screw 22. The space between the rotor 21 and the container'sinner wall defines the shear gap 23, in which the shear stress isbrought to bear on the product that is to be processed. The stationarycylinder consists of an inner cooling wall 25 and an outer coolingjacket 26. The cooling agent intake-feed takes place at the entry 31,and the cooling agent outlet-feed at the exit 32. The cylinder's frontwalls are formed by a storage-cover 27 and a seal-cover 28. They serveas support and resting-site for the rotor 21 that is adjustably drivenby the motor 3. The product intake-feed takes place at the entry 29, andthe efflux of the processed product at the exit 30.

The framework of the invention is flexible enough that the crystallizercan also be formed differently, for instance, the rotor could be cooledby an appropriate hollow-shaft apparatus. Jacket casing and rotor couldalso undergo cooling, if need be. What is vitally essential is thatheating must take place by means of the rotor-assisted introduction ofmechanical energy in the shear gap 23.

FIG. 3 shows melt enthalpy graphs which were arrived at based onDifferential Thermoanalysis (DSC). This analytical method allows theunambiguous differentiation and quantification of the γ, α, β', and βcrystal modifications arising for fats (in this case cocoa butter).

In order to achieve the requisite quality for foodstuffs containingcocoa butter, such as chocolate and fatty glazes (surface luster; breakswith a clean snap; melts smoothly), the cocoa butter, particularly thecocoa butter containing material system, needs to be crystallized insuch a way that the stable β-crystals are preferentially formed(approx.>50-60% β-crystals, <10% γ and α-crystals).

When processing and finishing the corresponding substances in theirfluid form (pouring, coating and blending), the aim is to work with assharply-defined degrees of viscosity as possible, so as to ensurereproducible product management and product quality. Substances of thiskind are as a rule processed and finished in their so-called"pre-crystallized" or "temperature-adjusted" form. This means that thecrystals receiving consideration in this state have to be predominantlystable β-crystals; and the proportional share of these crystals isregulated so that the substance that is to be processed as a fluid doesin fact possess the desired viscosity. As a rule the crystalline portionof pre-crystallized substances is of the order of approx.<5% by volume.The cooling temperature normally selected for pre-crystallization, forfluids containing cocoa butter, lies between 25-29° C. (substancetemperature) for a wall temperature range of 16-25° C. Processing timesvary between 10 and 30 minutes. A sharply-defined viscosity setting hasnot been possible up until now, but could only result by the temperaturesetting, since the operation is determined by retention-time (orflow-through rate).

In contrast to this traditional procedural method, the newlow-temperature shear crystallization procedure chooses extremely lowcrystallization temperatures (cf. FIG. 3: 2 examples, 16° C. and 4° C.).When cocoa butter has solidified statically at these temperatures,selected as examples, a very unstable "crystalline structure" (cf. FIG.3(1) and FIG. 3(2), predominantly γ and α -form) appears directly aftersolidification, which even after 24 hours' storage still exhibitsclearly unstable features (cf. FIG. 3(3) and FIG. 3(4), too few β;predominantly β' and α). The test sample, which solidified at 4° C.,crystallizes with increased instability after 24 hours.

Statically solidified test samples of this kind display a plethora ofqualitatively negative features (fat-whitening; breaks weakly;roughness).

If, under the same temperature conditions, a fixed introduction ofmechanical energy is supplied during low-temperature shearcrystallization, to "counter-control" temperature-inducedsolidification, a flawless product is achieved having predominantlystable crystalline forms (β) (cf. FIG. 3(5) and FIG. 3(6). Theexcellence of these products cannot be distinguished from those producedby traditional operating methods. Essential differences emerge fromcomparison with the traditional type of procedure, on the one hand, theadvantage of an easily specified viscosity setting, since theintroduction of mechanical energy as a control parameter allows quickand deliberate regulatory intervention in the operation; and on theother hand, very emphatically shortened processing times, which lie at 3and 6 seconds respectively in the example cited, and hence are reducedby a factor of>100 relative to traditional procedures. This results invery economical working quantities.

FIG. 4 shows a characteristic graph for cocoa butter, where for each oftwo fixed example viscosity settings (η=7×10⁻²,η=1.0×10⁻¹ Pas) theretention-time in the crystallizer is plotted as a function of thecooling temperature.

What is claimed is:
 1. A method for continuously controlling the textureand crystallization of a food material in the fluid state to produce afood material product whose crystalline parts are at least 50%β-crystals which comprise cooling the food material to a temperature offrom about 4° C. to about 16° C. in a continuous flow cooling cylinder,which cooling is conducted by means of a cooling cylinder wall, whichcooling cylinder wall is maintained at a temperature of from about 1° C.to about 70° C. below the freezing temperature of the food material, andsimultaneously subjecting the food material to a shearing stress forfrom about 3 to about 8.5 seconds, said shearing stress being applied tothe food material in a gap formed between the cooling cylinder wall anda rotor revolving within the cooling cylinder.
 2. The method of claim 1wherein the rotor has a scraper or a stripper.
 3. The method of claim 2wherein the stripper or scraper is in the form of a flat helix.
 4. Themethod of claim 1 wherein the regulation of the rotational speed of therotor and the shearing stress applied is effected by on an on-line orin-line viscosity measurement of the treated food material.
 5. Themethod of claim 4 wherein the viscosity of the food material is measuredby means of a bypass for the treated food material connected after anoutlet from the cooling cylinder.
 6. The method of claim 1 wherein thefree reaction volume in the gap amounts to 0.1 to 50 liters per 1,000l/h of throughput of the food material.
 7. The method of claim 1 whereinthe free reaction volume in the gap amounts to 0.25 to 10 liters per1,000 l/h of throughput of the food material.
 8. The method of claim 1wherein the food material produced has from about 50% to about 60% ofβ-crystals, and less than about 10% γ and α-crystals.
 9. The method ofclaim 1 wherein the food material comprises a fat containing substance.10. The method of claim 1 wherein the food material comprises achocolate mass.